SECTION ON CARDIOVASCULAR DISEASES

The predominant right precordial pattern seen in the electrocardiograms of patients with atrial septal defect is rsR′. Following closure of the defect there is a decrease in QRS duration and in the amplitude of the R wave. In a two year follow-up in this series there was no progressive diminution in QRS duration although the R wave continued to become smaller. The data indicate that delay in conduction in the right bundle branch system is due to stretching of the right ventricular muscle fibers and should be considered evidence of dilatation of the chamber.